When a tooth is devitalized it loses part of its elasticity and strength. The tooth becomes more fragile because it loses its live protein core and because it also becomes an anchor for a stem of a prosthesis. Often lateral forces on a crown or cap mounted on a peg seated in the bored-out tooth are mainly effective at an interface lying at an outer surface of the tooth. The bond at this interface eventually opens, allowing foreign matter to get into the tooth and causing localized action frequently breaking the peg or tenon off the prosthesis. Even if only one of several such anchors breaks, the entire prosthesis must be removed to do the necessary repair.
In a standard procedure a small screw is cemented into the bored-out tooth root. A ring is mounted on this screw and the cap or crown is built up on the ring.
It is also known to bore out the tooth to form therein a cavity whose shape corresponds to that of a tapered plug that is subsequently fitted to it. This arrangement often requires removal of vital strength-imparting dentin so that, even though the plug is very well seated, the tooth is in effect weakened by the installation.
All of the known procedures have in common that they add nothing to the strength of the tooth. In fact many known systems actually weaken the already reduced strength of the devitalized tooth.